Biosynthesis of Fatty Acids
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Questions and Answers

What is the primary location of fatty acid synthesis?

  • Cytosol
  • Adipose tissue and liver (correct)
  • Erythrocytes
  • Mitochondria
  • What is the source of acetyl CoA in fatty acid synthesis?

  • Oxidation of fatty acids
  • Oxidation of pyruvate
  • Degradation of ketone bodies
  • All of the above (correct)
  • Why is the coenzyme A portion of acetyl CoA not transported to the cytosol?

  • Because it is too large to cross the mitochondrial membrane
  • Because it cannot cross the mitochondrial membrane (correct)
  • Because it is not soluble in water
  • Because it is negatively charged
  • What is the purpose of citrate synthase in fatty acid synthesis?

    <p>To condense oxaloacetate and acetyl CoA</p> Signup and view all the answers

    Why can't the brain and erythrocytes use fatty acids as a source of fuel?

    <p>Because they require a constant supply of glucose</p> Signup and view all the answers

    What is the energy source for the carbon-carbon condensations in fatty acid synthesis?

    <p>Carboxylation and decarboxylation of acetyl groups</p> Signup and view all the answers

    What is the rate-limiting and regulated step in fatty acid synthesis?

    <p>Carboxylation of acetyl CoA</p> Signup and view all the answers

    What is required for the carboxylation of acetyl CoA to form malonyl CoA?

    <p>Biotin, ATP, and bicarbonate</p> Signup and view all the answers

    What is the effect of citrate on acetyl CoA carboxylase?

    <p>Allosteric activation</p> Signup and view all the answers

    What is the role of malonyl-CoA in regulating acetyl CoA carboxylase?

    <p>Allosteric inactivation</p> Signup and view all the answers

    What is the effect of epinephrine on acetyl CoA carboxylase?

    <p>Phosphorylation and inactivation</p> Signup and view all the answers

    What is the result of a prolonged consumption of a high-calorie, high-carbohydrate diet on acetyl CoA carboxylase synthesis?

    <p>Increased synthesis</p> Signup and view all the answers

    What is the enzyme responsible for the elongation of the fatty acid chain in 2-carbon increments?

    <p>Fatty acid synthase</p> Signup and view all the answers

    What is the function of acyl carrier protein (ACP) in fatty acid synthase?

    <p>Covalently binds to Pantothenic acid and carries acetyl and acyl units</p> Signup and view all the answers

    What is the product of the carboxylation of acetyl CoA?

    <p>Malonyl-CoA</p> Signup and view all the answers

    What is the subcellular location of the first step of fatty acid biosynthesis?

    <p>Mitochondria</p> Signup and view all the answers

    Study Notes

    Fatty Acid Synthesis (Lipogenesis)

    • Excess carbohydrates and proteins can be converted to fatty acids and stored as triglycerols.
    • Fatty acid synthesis occurs primarily in the liver and adipose tissue.

    Stage 1: Mitochondria

    • Acetyl CoA is produced from:
      • Oxidation of pyruvate
      • Degradation of fatty acids
      • Degradation of ketone bodies
    • Acetyl CoA is transferred from the mitochondrial matrix to the cytosol in the form of citrate.

    Stage 2: Cytosol

    • Citrate is cleaved by ATP-citrate lyase to produce cytosolic acetyl CoA and oxaloacetate.
    • Carboxylation of acetyl CoA to form malonyl CoA requires:
      • Acetyl CoA carboxylase
      • Biotin
      • ATP
      • Bicarbonate (HCO3-)
    • Acetyl CoA carboxylase is a multienzyme protein consisting of 3 identical functional subunits.

    Regulation of Acetyl CoA Carboxylase

    • Short-term regulation:
      • Citrate: allosteric activation
      • Palmitoyl-CoA: allosteric inactivation (feedback inhibition)
      • Malonyl-CoA: allosteric inactivation
      • Reversible phosphorylation: regulated by cAMP-dependent protein kinase
    • Long-term regulation:
      • High-calorie, high-carbohydrate diets: increase acetyl CoA carboxylase synthesis and fatty acid synthesis
      • Low-calorie diet or fasting state: decrease acetyl CoA carboxylase synthesis and fatty acid synthesis

    Fatty Acid Synthesis (Continued)

    • Step 3: Elongation of the fatty acid chain (in 2-carbon increments) by fatty acid synthase.
    • Fatty acid synthase (FAS):
      • Dimeric enzyme
      • Each monomer composed of:
        • 7 different enzymatic activities
        • Acyl carrier protein (ACP): covalently binds to pantothenic acid, carrying acetyl and acyl units on its terminal thiol (-SH) group.

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    Description

    Learn about the process of fatty acid synthesis, where excess carbohydrates and proteins are converted to fatty acids and stored as triglycerols, primarily in the liver and adipose tissue.

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